It is known from the state of the art that organo-modified siloxanes, such as polyether siloxanes or polysiloxanes, which have substituents with anionic, cationic or amphoteric groups, an appropriate structure and a balanced ratio of hydrophilic and hydrophobic groups, can lower the surface tension of aqueous solutions to a pronounced extent.
Surfactants with at least silicon atoms are disclosed in the German patent 41 41 046. They correspond to the general formula ##STR2##
wherein
R.sup.1 is a methyl or phenyl group, with the proviso that at least 90% of the R.sup.1 groups are methyl groups, PA1 R.sup.2 is R.sup.1 or --(CH.sub.2).sub.6 --OSO.sub.3.sup.31.M.sup.+, wherein PA1 M.sup.+ is an alkali, 1/2alkaline earth or optionally an alkyl-substituted ammonium ion, PA1 R.sup.3 is R.sup.1 or R.sup.2, PA1 a is 0 to 5, and PA1 b is 0 to 5. PA1 (Bu=Butyl, M=Sn, Si), PA1 R.sup.1, R.sup.2 and R.sup.3 in the molecule are the same or different and represent aliphatic or aromatic hydrocarbon groups, PA1 R.sup.4 is a divalent hydrocarbon group with 4 to 12 carbon atoms and a lateral hydroxyl group, wherein the hydrocarbon group can be interrupted by an ether oxygen, and PA1 R.sup.5 is a hydrophilic, ionic group. PA1 R.sup.5 is an ionic group having the formula ##STR9## PA1 a) epoxides, which have a olefinic double bond, are reacted by means of an addition reaction in the presence of a hydrosilylation catalyst with silanes of the general formula ##STR11## PA1 and PA1 b) the epoxide ring of the silane-modified epoxides is opened by a known reaction and the product obtained is PA1 as wetting agents: PA1 in preparations for the treatment of plants (agricultural formulations); for improving the wetting of substrates with a low surface-free energy, such as polyethylene and polypropylene surfaces; for use in the paint industry; for the production of photographic films; in galvanizing technology; PA1 as dispersant: PA1 for dispersion paints, pigments and fillers; PA1 as emulsifiers or additives in the textile industry for the production of textile auxiliaries, fabric softeners, lubricants, antistatic preparations; as a dyeing auxiliary; PA1 as surfactants in general: PA1 for use in fire extinguishers; as foam stabilizers; as surface-active additives to high speed printing inks, adhesives, dispersion adhesives, melt adhesives; for use in detergents; as additives for industrial cleaners; PA1 as raw materials for use in cosmetics, for example, in grooming aids, shampoos, shower gels; PA1 in technical applications and in the household: PA1 anti-condensation agent for use in dishwashing detergents, laundry detergents, toilet cleaners, automatic gloss emulsions.
with the proviso that in the average molecule, at least one R.sup.2 or R.sup.3 group is a --(CH.sub.2).sub.6 --OSO.sub.3.sup.-.M.sup.+, PA2 b1) sulfonated, or PA2 b2) quaternized by reaction with tertiary amines having the formula ##STR12## PA2 in the presence of an acid YH, or PA2 b3) converted by a reaction with a compound of the formula ##STR13## PA2 into the betaine.
The selected siloxane hexyl sulfates, which are trisiloxane hexyl sulfates in the event that three silicon atoms are present, bring about a pronounced lowering in the interfacial tension of neutral aqueous media to values of about 21 mN/m. However, they are unstable in acidic or alkaline solutions and, due to the hydrolysis of the Si--O--Si bonds and renewed condensation of the hydrolysis products to higher molecular weight oligomers, very rapidly lose their effectiveness and partly become insoluble in aqueous media.
Surfactants with a low content of silicon atoms are furthermore described in the European publication 0 367 381 (A2) and the British patent 1,520,421.
The European publication 0 367 381 (A2) relates to organosilicon compounds of the general formula ##STR3##
wherein the R groups, independently of one another, represent an alkyl, aryl, halogenated alkyl or halogenated aryl group with up to 18 carbon atoms, each R' groups represents an alkylene group, which separates adjacent silicon atoms by up to 6 carbon atoms from one another, and the R" groups independently of one another represent R or, when a=0, the R.sub.3 SiR' group. Z is a hydrophilic substituent, which contains sulfur, nitrogen or phosphorus, a carboxy-functional group or the salt of such a group, while a has a value of 0, 1 or 2.
It follows from this that, by definition, the organosilicon group contains at least two silicon atoms. The synthesis of these carbosilanes is relatively expensive and is carried out, for example, by a reaction similar to a Grignard reaction. After that, carbosilane surfactants with a quaternary, sulfonate or betaine structure are synthesized by means of the hydrosilylation of, for example, allyl glycidyl ether or allylamine. The substances, so obtained, lower the surface tension of a 1% solution in distilled water to 23 to 25 mN/m.
Carbosilanes surfactants and their synthesis are disclosed in the British patent 1,520,421. They have the general formula ##STR4##
wherein R is a methyl, ethyl, propyl or trifluoropropyl group, with the proviso that at least 50% of the R groups are methyl groups, R' is an alkyl group with 1 to 6 carbon atoms and R" is a divalent aliphatic hydrocarbon group with 2 to 6 carbon atoms, which connects Q and the adjacent silicon atom by a bridge of at least 2 carbon atoms. Q is an --O(C.sub.2 H.sub.4 O).sub.c X, wherein c has a value of 3 to 12 and X is a hydrogen group, R'" group, ##STR5##
in which R'" is an alkyl group with 1 to 5 carbon atoms, a has a value or 1 or 2 and b a value of 2 or 3.
By definition, at least two silicon atoms must be present here also. In application tests, these compounds show remarkable foaming properties.
In this connection, it was known to those skilled in the art that, within groups of these known carbosilanes with comparable structure, the surfactant properties of the compounds deteriorate as the number of silicon atoms decreases, particularly from 4 to 3 or 2. This observation is reflected in the theory of Neumann (A. W. Neumann, D. Renzow, Zeitschrift f. Phys. Chem., New Issue 68, 11, (1969)), which states that the permethylated surface of the siloxane backbone is responsible for lowering the surface tension of aqueous solutions to below 30 to 40 mN/m.
Furthermore, reference is made to the Japanese publications of H. Maki et al. in YUKAGAGU 19, No. 4, page 51 ff. and YUKAGAGU 19, No. 11, page 23 ff., both from the year 1970, in which defined compounds of the formulas EQU (CH.sub.3).sub.3 Si(CH.sub.2).sub.3 (C.sub.2 H.sub.4 O).sub.n H
and EQU ((CH.sub.2).sub.4).sub.3 Si(CH.sub.2).sub.3 (C.sub.2 H.sub.4 O).sub.m H
are described, wherein n=4.0 or 7.7 and m=10 or 17. However, these compounds lower the interfacial tension of a 0.1% by weight solution only to values of not less than 26.5 mN/m.
Likewise, quaternary nitrogen compounds having the formula EQU Bu.sub.3 M(CH.sub.2).sub.3 N.sup.+ (CH.sub.3).sub.3 Cl.sup.-
which, admittedly, are bacteriostatic but not very surface active, are described in these Japanese publications. The best representatives of these quaternary compounds lower the surface tension of a 1% aqueous solution to 32 mN/m.
The present invention is based on the surprising finding that, in contrast to general theoretical or factual knowledge, as expressed, for example, in the Neumann theory, selected silanes, that is, compounds with only a single silicon atom, but in which the ratio of hydrophilic to hydrophobic parts of the molecule is balanced, lower the surface tension of water exceeding effectively and, in contrast to the siloxane surfactants, are resistant to hydrolysis for days and weeks even in acidic and alkaline media. A further and not foreseeable advantage of the inventive silanes is their complete biodegradability, which makes them particularly suitable for use as surfactants. Such a profile of properties could not be derived from the state of the art and contradicts the previously customary assumptions concerning structural requirements, which organosilicon compounds should fulfill in order to show interfacial tension-lowering properties in aqueous systems.